The present invention relates to oscilloscopes of the type providing a digital display of adjustable parameters relating to oscilloscope operation and particularly to a method and apparatus for adjusting the parameters.
A major feature of delayed sweep oscilloscopes is the ability to initiate a second (B) sweep at a selectable point along a first (A) sweep to view an event of interest with closer scrutiny and to provide greater precision in making timing measurements. Two principal delaying modes have been established: delay-by-time, and delay-by-events. In the delay-by-time mode, a selectable voltage is typically provided by a precision linear potentiometer and compared with a delaying sweep ramp voltage to generate a delayed sweep trigger at any point in time along the delaying sweep. In the delay-by-events mode, a particular event, such as one pulse in a data stream, is selected for initiation of the delayed sweep. Adjusting the desired event count limit, however, has always been somewhat cumbersome or difficult.
One particular prior art method of delay-by-event count adjustment is taught in U.S. Pat. No. 3,843,873 to Bevile et al. Here, a variable-frequency clock, the rate of which is selected by a front-panel control, is utilized to increment or decrement a reversible counter thereby to select an event count at which a delayed sweep will be activated. Not only are many mechanical and electrical parts required for this technique, but the actual selection requires skill and patience on the part of an operator.
Another feature of some oscilloscopes is the ability to determine the condition of a set of data input lines and to initiate a sweep when the data is recognized as a preselected word. In some delayed sweep oscilloscopes the sweep may be delayed until after the word has been recognized a set number of times. In the past, methods to modify the word to be recognized have involved the use of front-panel setups with toggle switches, keyboards, thumbwheels, and LED (light-emitting diode) displays also requiring substantial space and mechanical and electrical parts and often being slow or cumbersome to use.
What is needed and what would be useful is a method and apparatus for rapidly modifying displayed parameters which utilizes controls on the oscilloscope front panel also used for other functions.